1. Field of the Invention
An aspect of the present invention relates to a voltage step-down circuit in a semiconductor memory.
2. Description of the Related Art
In the semiconductor devices such as the semiconductor memory, or the like, for the purpose of compatibility between the finer patterning in manufacturing processes and the standardization of a power supply voltage, a plurality of voltage step-down circuits for converting a power supply voltage supplied from the outside into internal power supply voltages suitable for applied manufacturing processes respectively are used nowadays (see JP-A-2000-200483, for example).
As the voltage step-down circuit, various circuit configurations are used. The voltage step-down circuit generates the internal power supply voltage from the power supply voltage and operates in both an active state for supplying a large current to a load circuit, such as a memory, and a standby state for suppressing the current supplied to the load circuit. As one configuration, there is the circuit configuration equipped with a source follower type transistor (Tract) operated only in the active state and a source follower type transistor (Trstby) operated in both the standby state and the active state. In such voltage step-down circuit, it has been considered conventionally that a current is supplied from the power supply voltage to the internal power supply voltage mainly by Tract in the active state whereas only by Trstby in the standby state.
However, when an operating state of the voltage step-down circuit is switched from the active state to the standby state, the charges that are accumulated in an inversion layer and a drain region of Tract that is larger than Trstby flow into the internal power supply voltage, and thus another current supply source is generated in the standby state in addition to Trstby. Therefore, such a problem has arisen that an extra voltage rise is brought about in the standby state. Since this phenomenon takes place every time when the operating state is switched from the active state to the standby state, such a problem has arisen that a greater voltage variation is generated as the operating state is switched at a higher cycle.